Local allergen challenge in patients with allergic rhinitis, bronchial asthma, allergic conjunctivitis and atopic dermatitis has been shown to result in rapid elevation of prostaglandin D2 “(PGD2)” levels in nasal and bronchial lavage fluids, tears and skin chamber fluids. PGD2 has many inflammatory actions, such as increasing vascular permeability in the conjunctiva and skin, increasing nasal airway resistance, airway narrowing and eosinophil infiltration into the conjunctiva and trachea.
PGD2 is the major cyclooxygenase product of arachidonic acid produced from mast cells on immunological challenge [Lewis, R A, Soter N A, Diamond P T, Austen K F, Oates J A, Roberts L J II, Prostaglandin D2 generation after activation of rat and human mast cells with anti-IgE, J. Immunol. 129, 1627-1631, 1982]. Activated mast cells, a major source of PGD2, are one of the key players in driving the allergic response in conditions such as asthma, allergic rhinitis, allergic conjunctivitis, allergic dermatitis and other diseases [Brightling C E, Bradding P, Pavord I D, Wardlaw A J, New Insights into the role of the mast cell in asthma, Clin. Exp. Allergy 33, 550-556, 2003].
Many of the actions of PGD2 are mediated through its action on the D-type prostaglandin (“DP”) receptor, a G protein-coupled receptor expressed on epithelium and smooth muscle. In asthma, the respiratory epithelium has long been recognized as a key source of inflammatory cytokines and chemokines that drive the progression of the disease [Holgate S, Lackie P, Wilson S, Roche W, Davies D, Bronchial Epithelium as a Key Regulator of Airway Allergen Sensitization and Remodelling in Asthma, Am J Respir Crit Care Med. 162, 113-117, 2000]. In an experimental mouse model of asthma, the DP receptor is dramatically up-regulated on airway epithelium on antigen challenge [Matsuoka T, Hirata M, Tanaka H, Takahashi Y, Murata T, Kabashima K, Sugimoto Y, Kobayashi T, Ushikubi F, Aze Y, Eguchi N, Urade Y, Yoshida N, Kimura K, Mizoguchi A, Honda Y, Nagai H, Narumiya S, prostaglandin D2 as a mediator of allergic asthma, Science 287, 2013-2017, 2000]. In knockout mice, lacking the DP receptor, there is a marked reduction in airway hyperreactivity and chronic inflammation, two of the cardinal features of human asthma [Matsuoka T, Hirata M, Tanaka H, Takahashi Y, Murata T, Kabashima K, Sugimoto Y, Kobayashi T, Ushikubi F, Aze Y, Eguchi N, Urade Y, Yoshida N, Kimura K, Mizoguchi A, Honda Y, Nagai H, Narumiya S, Prostaglandin D2 as a mediator of allergic asthma, Science 287, 2013-2017, 2000].
The DP receptor is also thought to be involved in human allergic rhinitis, a frequent allergic disease that is characterized by the symptoms of sneezing, itching, rhinorrhea and nasal congestion. Local administration of PGD2 to the nose causes a dose dependent increase in nasal congestion [Doyle W J, Boehm S, Skoner D P, Physiologic responses to intranasal dose-response challenges with histamine, methacholine, bradykinin, and prostaglandin in adult volunteers with and without nasal allergy, J Allergy Clin Immunol. 86(6 Pt 1), 924-35, 1990].
DP receptor antagonists have been shown to reduce airway inflammation in a guinea pig experimental asthma model [Arimura A, Yasui K, Kishino J, Asanuma F, Hasegawa H, Kakudo S, Ohtani M, Arita H, Prevention of allergic inflammation by a novel prostaglandin receptor antagonist, S-5751, J Pharmacol Exp Ther. 298(2), 411-9, 2001]. PGD2, therefore appears to act on the DP receptor and plays an important role in elicitation of certain key features of allergic asthma.
DP antagonists have been shown to be effective at alleviating the symptoms of allergic rhinitis in multiple species, and more specifically have been shown to inhibit the antigen-induced nasal congestion, the most manifest symptom of allergic rhinitis [Jones, T. R., Savoie, C., Robichaud, A., Sturino, C., Scheigetz, J., Lachance, N., Roy, B., Boyd, M., Abraham, W., Studies with a DP receptor antagonist in sheep and guinea pig models of allergic rhinitis, Am. J. Resp. Crit. Care Med. 167, A218, 2003; and Arimura A, Yasui K, Kishino J, Asanuma F, Hasegawa H, Kakudo S, Ohtani M, Arita H, Prevention of allergic inflammation by a novel prostaglandin receptor antagonist, S-5751. J. Pharmacol. Exp. Ther. 298(2), 411-9, 2001].
DP antagonists are also effective in experimental models of allergic conjunctivitis and allergic dermatitis [Arimura A, Yasui K, Kishino J, Asanuma F, Hasegawa H, Kakudo S, Ohtani M, Arita H, Prevention of allergic inflammation by a novel prostaglandin receptor antagonist, S-5751. J. Pharmacol. Exp. Ther. 298(2), 411-9, 2001; and Torisu K, Kobayashi K, Iwahashi M, Nakai Y, Onoda T, Nagase T, Sugimoto I, Okada Y, Matsumoto R, Nanbu F, Ohuchida S, Nakai H, Toda M, Discovery of a new class of potent, selective, and orally active prostaglandin D2 receptor antagonists, Bioorg. & Med. Chem. 12, 5361-5378, 2004].
Patent application WO 2006044732 (hereinafter the '732 publication), hereby incorporated by reference, discloses pyrimidines that have valuable pharmaceutical properties including, in particular, the ability to associate with and regulate the DP receptor. The '732 publication discloses pyrimidines of Formula (I),
their preparation, pharmaceutical compositions containing these compounds, and their pharmaceutical use in the treatment of disease states capable of being modulated by the inhibition of the prostaglandin D2 receptor. Furthermore, the '732 publication specifically discloses and claims 2-(3-{6-[2-(2,4-dichloro-phenyl)-ethylamino]-2-methoxy-pyrimidin-4-yl}-phenyl)-2-methyl-propionic acid (hereinafter “the free form”). The '732 publication also provides a general description of a wide variety of acid addition salts and base addition salts of compounds according to the invention, and assorted working examples limited to the preparation of hydrochloride salts and sodium salts. More specifically the hydrochloride salt and sodium salt of 2-(3-{6-[2-(2,4-dichloro-phenyl)-ethylamino]-2-methoxy-pyrimidin-4-yl}-phenyl)-2-methyl-propionic acid are disclosed. The '732 publication, however, does not specifically disclose a dihydrogen phosphate salt of 2-(3-{6-[2-(2,4-dichloro-phenyl)-ethylamino]-2-methoxy-pyrimidin-4-yl}-phenyl)-2-methyl-propionic acid.